The ultimate goal of the research described in this application is to develop an economical, safe and effective countermeasure to defend the American public from a bioterrorist attack by botulinum toxin. We aim to be the manufacturer of an antibody or antibody mixture, derived form transgenic plants; that win effectively neutralize botulinum toxin and will supplant the current antitoxin, which is available only in limited supply. We believe that transgenic plants offer the best system for producing high-quality antitoxin at the lowest possible cost. Botulinum toxins (BoNT) are extremely potent neurotoxins produced by anaerobic bacteria of the genus Clostridium. Botulinum neurotoxin A (BoNT/A) is the deadliest biological substance known, with an LD50 between 1-5 ng/kg. Due to their potency and ease of production using unsophisticated techniques, BoNTs have been intentionally produced for use as biological warfare agents and weapons of terror. In Phase I we produced three high-affinity humanized plantibodies against botulinum neurotoxin A (BoNT/A) using transgenic tobacco plants and showed that they are physically very similar to their CHO-cell produced counterparts, that they bind to BoNT/A with similar affinity, and that they protect mice from thousands of LD50s of BoNT/A. We have five aims for Phase II: 1. Produce, in transgenic tobacco, three anti-botox IgG plantibodies with modified Fc sequences to enhance binding to Fc receptors; 2. Examine efficacy, toxicity, and pharmacokinetics of Fc-modified IgG in a mouse model of toxin neutralization; 3. Produce cGMP grade plantibodies for animal and human studies; 4. Examine pharmacokinetics/toxicology of anti-botox IgG plantibodies, and efficacy of toxin neutralization, in a non-human primate model. 5. Examine safety of plant- made antibody in human Phase I clinical trials. Botulinum toxin is the deadliest substance known, and would be easy for a terrorist to produce and use to cause large numbers of casualties. This makes developing an effective and economical countermeasure to protect the public a public health priority. The research supported by this application will lay the groundwork for using plants to produce a highly protective, safe and economical antitoxin therapy. [unreadable] [unreadable]